Most likely you run with a framrate to far away from what your monitor can handle. If you run off cheaper monitors like I am and they are at 60hz means 84FPS wont show you more than 60 frames and then they change to fast for your monitors so you wont even see 60 full frames.
Putting on vsync might help, but in most cases that causes input lag, my way of resolving it and to avoid a lot of screen tearing is just above 60fps, I have mine on 63 and the stuttering I had using 67-115fps are gone.
You could go up to 120 witch is 60 multiplied with 2, meaning you see only 60fps, but the machine is creating 2 frames to fit into those 60hz. But my computer work less with 63fps and I can have more graphics enabled, even on tracks like Suzuka and Spa, and I'm not any slower, I worked on it a lot, and if you didn't even figured out how to turn it back to 32bit you didn't check a lot before you want to give up..
Although 32bit wont help you a bit.